<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .parent{
            width:300px;
            height: 300px;
            background: red;
        }
        .one{
            margin-top: 50px;
            width:100px;
            height:100px;
            background: blue;
            margin-bottom: 50px;
        }
        .two{
            margin-top: 70px;
            width:100px;height:100px;background: pink;
        }
        .row::before{
            content:"";
            display: table;
        }
    </style>
</head>
<body>
    <!-- bug:子元素作用父元素的第一个元素,给它margin-top没用
        它的父级移动
     -->
    <div class="parent row">
        <div class="one">

        </div>
        <div class="two">

        </div>
    </div>  
    <!-- 两个兄弟元素之间margin重合的问题,如果两个值相等那么取中间值,如果一个值大,取那个大的值-->
</body>
</html>